Background: This study assessed the ability of end tidal carbon dioxide (ETCO2) in predicting in-hospital mortality and ICU admission compared to standard vital signs at ED triage. Additionally, ETCO2 was correlated with other laboratory measures of acidosis.
Methods: This prospective observational study enrolled a convenience sample of adult patients presenting to the ED of a tertiary care level 1 trauma center over 30 months. Patients had initial vital signs of temperature (Temp), respiratory rate (RR), systolic and diastolic blood pressure (SBP and DBP), heart rate (HR), oxygen saturation (SpO2) measured along with exhaled ETCO2 at triage. Patients were followed throughout their hospital stay. Outcome measures included in- hospital mortality, ICU admission and correlations with laboratory measures of poor perfusion and/or acidosis such as serum lactate, sodium bicarbonate (HCO3) and anion gap. 95%CI’s were calculated along with area under the ROC curve (AUC) and Spearman’s rho.
Results: There were 1136 patients prospectively enrolled and 1091 patients with outcome data available. Patient mean age was 56 (SD19) and 53% were male. Mean levels of ETCO2 at triage in all patients was 34 (95%CI 33-34) mmHg. There were 26 (2.4%) patients with in-hospital mortality and mean ETCO2 levels in survivors versus non-survivors was 34 (33-34) versus 22 (18- 26)(p<0.001). The AUC for predicting in-hospital mortality for ETCO2 was 0.82 (0.72-0.91); AUC for temp was 0.55 (0.42-0.68); AUC for RR 0.59 (0.46-0.73); AUC for SBP was 0.77 (0.67- 0.86); AUC for DBP was 0.70 (0.59-0.81); AUC for HR was 0.76 (0.66-0.85); and AUC for SpO2 was 0.53 (0.40-0.67). There were 64 (6%) patients admitted to the ICU and the ETCO2 AUC for predicting ICU admission was 0.75 (0.67-0.80); AUC for temp was 0.51 (0.42-0.59); RR 0.56 (0.47-0.65); SBP was 0.64 (0.56-0.72); DBP was 0.63 (0.55-0.71); HR was 0.66 (0.58-0.73); and SpO2 was 0.53 (0.45-0.61). Correlations between expired ETCO2 and serum lactate, HCO3, and anion gap were rho=-0.25 (p<0.001), rho=-0.22 (p<0.001), and rho=-0.21 (p<0.001) respectively.
Conclusion: ETCO2 was a remarkably better predictor of in-hospital mortality and ICU admission than the standard vital signs at ED triage. ETCO2 also correlated significantly with measures of acidosis. An ongoing study is evaluating the role of ETCO2 as a triage vital sign.